fetch-pack: sort incoming heads

There's no reason to preserve the incoming order of the
heads we're requested to fetch. By having them sorted, we
can replace some of the quadratic algorithms with linear
ones.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/fetch-pack.c

@@ -1057,6 +1057,11 @@ int cmd_fetch_pack(int argc, const char **argv, const char *prefix)
 	return ret;
 }
 
+static int compare_heads(const void *a, const void *b)
+{
+	return strcmp(*(const char **)a, *(const char **)b);
+}
+
 struct ref *fetch_pack(struct fetch_pack_args *my_args,
 		       int fd[], struct child_process *conn,
 		       const struct ref *ref,
@@ -1076,8 +1081,11 @@ struct ref *fetch_pack(struct fetch_pack_args *my_args,
 			st.st_mtime = 0;
 	}
 
-	if (heads && nr_heads)
+	if (heads && nr_heads) {
 		nr_heads = remove_duplicates(nr_heads, heads);
+		qsort(heads, nr_heads, sizeof(*heads), compare_heads);
+	}
+
 	if (!ref) {
 		packet_flush(fd[1]);
 		die("no matching remote head");